1. Field of the Invention
The present invention relates to improvements in specimen-container racks of the type used to support multiple containers, e.g., test tubes, of liquid specimens for analysis or processing by a clinical instrument. More particularly, it relates to improvements in specimen-container racks of the type that are adapted to be transported over a rack-supporting surface via magnetic forces.
2. The Prior Art
It is known in the art to perform diagnostic tests on various liquid biological specimens, e.g., whole blood, serum, urine, spinal fluids, etc., using different automated clinical instruments. The specimens to be analyzed by such instruments are commonly collected in various types of test tubes or containers. Each container is normally sealed at its top by a puncturable rubber cap through which a movably-mounted aspiration probe of a clinical instrument can enter and withdraw a desired aliquot of specimen for processing. Typically, five or six specimen-containers, each bearing encoded patient and test information in the form of a bar code or the like, are supported for aspiration by a single rack or cassette. The rack serves to align, center and equally space the containers to simplify the required movement of the instrument's aspiration probe in order to gain access to the interior of each container. In some instruments, the aspiration probe is movably-mounted on the exterior of the instrument housing; with such instruments, an external specimen-transport device or module can be used to present specimen-container racks to a specimen-aspiration station or location where the aspiration probe can sequentially aspirate specimens from each container.
U.S. Pat. No. 5,720,377, filed in the names of Lapeus et al., discloses a specimen-transport module of the type noted above. The module operates to present individual racks of specimen-containers to an externally-accessible aspiration probe of an associated clinical instrument. The module generally comprises three interrelated trays, viz., (a) an elongated input tray that is adapted to receive and temporarily store a linear queue of specimen-container racks, (b) a movably-mounted process tray that is adapted to receive racks of specimen-containers, one at a time, from the input tray and to present them to a location for specimen-aspiration and testing, and (c) an elongated output tray that is adapted to receive processed racks one at a time from the process tray and to temporarily store such racks in a linear output queue for subsequent retrieval. The input and output trays are linearly aligned, end-to-end, and each tray is provided with linear guides that interact with features on the racks to align the received racks to form the respective linear queues in which the racks are arranged side-by-side (cf., end-to-end). The process tray is positioned adjacent to the input and output trays and extends parallel to these trays. Upon reaching a loading position in the input tray, the foremost rack in the input queue is physically urged, edgewise, out of the tray and into an awaiting empty slot of the processing tray. Upon processing each container in a rack contained by the processing tray, the latter is advanced linearly, parallel to the input and output trays, to a location where the processed rack can be physically pushed, again edgewise, into an empty space on the output tray. Another pusher mechanism then operates to push together all the racks in the output tray to form a closely-spaced output queue of racks arranged side-by-side.
In the above-noted patent disclosure, each of the racks of the input queue is forwardly advanced over the rack-supporting surface of the input tray by a magnetic transport system that underlies the input tray. The input tray is made of a nonmagnetic material (in this case, aluminum), and each specimen-container rack carries one or more (preferably two) magnetically-attractive members in its base portion. The magnetic transport system that underlies the input tray comprises a pair of parallel conveyor belts, each carrying a plurality of permanent magnets at equally spaced locations along the belt length. The belts are trained about spaced pulleys, and one reach of each of the belts is closely spaced from the underside of the input tray, extending in the intended direction of rack-travel, i.e., in a direction parallel to the linear guides on the tray. As the belts are driven along their respective endless paths, the respective magnetic fields associated with two of the permanent magnets, one carried by each belt, passes through the input tray and approaches the rack from the side, at the two locations where the magnetically-attractive members are located. Upon reaching a position where the permanent magnets of the transport mechanism and the magnetically-attractive members of the racks become magnetically coupled, the racks slide along the surface of the input tray following the movement of the permanent magnets beneath the tray. The racks are thus magnetically advanced along a linear path defined by the rack's guides until the foremost rack in the input tray has reached a position in which it can be mechanically advanced edgewise into the process tray.
In the rack described above, the magnetically-attractive members are located in the rack's base portion in the vicinity of the ends of the rack. Each member is either tapered in thickness across the width of the rack or arranged at an angle with respect to the rack's bottom surface such that, as the permanent magnets of the conveyor belt system approach the rack from the side, the magnetic force between the magnets and the magnetically-attractive members gradually increases until the permanent magnets are either directly opposite the thickest portion of each of the magnetically-attractive members, or they are opposite to those portions of the members that are closest to the bottom surface of the rack and, hence, closest to the magnets (in both cases).
The specimen-container rack described above, while useful in a unidirectional magnetic transport system, is not well suited for use with a magnetic transport system adapted to transport racks in mutually perpendicular directions, i.e., in an X/Y plane. In an X/Y transport system, the magnetic force between the rack and transport system should be independent of the direction in which the rack is to be transported, rather than being optimized for transport in one direction only.